1. Field of the Invention
The present invention relates to an optical vision device used in medical diagnosis, and more particularly to a inspection device for observing, recording and analyzing the eyes of patients by detecting vertical, horizontal and rotational eye movements.
2. Prior Art
Observation of a patient's eye movements is an indispensable diagnostic tool for clinical investigation of inner-ear, balance and central nerve dysfunction. Dizziness and disorders of these systems have a recognized relationship, and by testing the eye movements of a patient, symptoms of such disorders can be found. Thus, a variety of eye movement detecting devices are widely used.
As ordinary inspection devices, there are so-called "ENG" and "EOG" devices which utilize characteristic differences in the electrical potential between the cornea and retina. In such devices, electrodes are set on the surface of the skin near the eye sockets so that the electrical potential difference created by eye movements is collected and recorded through the electrodes. In the ENG device, such difference is outputted as an alternating current so that eye movement velocity is recognized, and in the EOG device, the differences are outputted as a direct current so as to indicate eye movement fluctuations.
In another device called a "PRNG," an infrared ray is radiated to the right and left sides of the eyeballs, and the intensity of light reflected on the cornea and retina is observed and then the eye movements are recorded on a polygraph. Another device which private practitioners often use is a Franzel lens device. In this device, eye movements are directly observed via a 20 diopter lens equipped with a light source. Recently, such a device is sold with a TV camera attached.
In addition, there is another device defined as a "search coil." In this device, a patient wears contact lenses having coils therein, and eye movement signals are outputted via a magnetic field device. In a recently developed device, an infrared ray TV camera catches reflected light from the infrared ray radiation from the eyes to obtain signals of eye movement through the camera. Devices of this type are disclosed in publications such as Ann Otol Phinol Laryngol, 1977 and Acta Otolarygol, 1987.
However, tests conducted with the ENG and EOG devices are likely to be affected by noise caused by the electrical potential of the skin, since the electrical potential of the cornea-retina and skin are the same. Also, in such devices, fluctuations in potentials often result, and unless the vertical and horizontal lead lines from the electrodes on the skin are crossed at completely right angles, fluctuations can easily occur thus decreasing the accurate detection. Moreover, cycloduction movement of the eyeballs cannot be tested, and also the test must be performed in a dark room. Furthermore, since the electrical potential of the cornea and retina are unsteady, frequent corrections and adjustments are required. In addition, ENG and EOG devices are easily affected by blinking and movements of the eyelids, and when eyes are closed to avoid visual fixation (involuntary viewing at one position), vertical eye vibrations (eye movement in the vertical direction) occurs, and therefore, true eye movement cannot be observed. Also, since a separate target display is necessary to conduct tests with these devices, a fairly large space is required.
A test with the PENG device is likely to be affected by blinking or eyelid movements, and since the test must be performed while the eyes are open, visual fixation can easily occur and nystagmus (eyeball movement) may be lowered. Although there is no affect from the electrical potential of the skin, the test must be conducted in a dark room, as in the case of ENG and EOG devices, and a separate target display is still required. Furthermore, the cycloduction movement cannot be tested either.
With the Franzel lens device, cycloduction can be confirmed visually, and the test can be performed in a lighted room. However, the eyes cannot follow a moving display target, and visual fixation cannot be completely eliminated. Besides these disadvantages, it is impossible to obtain continuous recording and analysis of the reactions of eye movements with this device.
The "search coil device" requires that patients wear contact lenses, and the test must be done inside a magnetic-field device. Accordingly, patient's movement tends to be minimal, and natural eye movement cannot be observed. In addition, devices which use reflected light caused by radiation of infrared ray, as disclosed in the noted publications, require dark rooms, and complicating testing procedure.